Noisy system during heat cycle

My Boilermate III system is very noisy, but only during the final few minutes of the cycle to heat up the thermal store. The noise can best be described as a loud tapping / hammering sound. Difficult to pinpoint the exact location - it could be coming from the boiler (a Potterton Suprima 40) but more likely from the Boilermate unit. The noise only occurs when the boiler flame is on. Occasionally, the same noise occurs when the central heating has been on for a long time, but never as loud. A few weeks ago, I had a new system pump fitted as the entire system was shutting down on a regular basis after overheating, accompanied by a very loud hammering sound. The engineer thought that the old system pump was failing / shutting down, causing the overheat. The new pump seems to be keeping the system running, but we are experiencing this new noise which is very annoying, especially overnight when the thermal store is heated 2 or 3 times. The whole system. Boilermate & Boiler, is approx 8 years old. Any ideas on the cause of this fault will be much appreciated ..

Hi andersj2,

Odd symptoms... Sounds to me as though the pump over-run has stopped working perhaps. New control board might be needed. Would need to come to site and test it to be sure. Where are you? Can this fault be reproduced reliably?

Cheers, Mike